Blasting machine



Sept; l9, 1944. 'J. E. FOSTER BLASTING MACHINE Filed A ril 18, 1942 3Sheets-Sheet l Sept. 19, 1944. J. E. FOSTER BLASTING MACHINE Filed April18, 1942 3 Sheets-Sheet 2 v INVENTOR. dc/4 as E. Fosrsx? Patented Sept.19, 1944 UNITED STATES PATENT OFFICE (Granted under the act of. March 3,1883, as amended April 30, 1928; 3'10 0. G. 757) 12 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

My invention relates to blasting machines, particularly intended forprojecting an abradant material, such as shot or grit or the like, in apredetermined direction.

One object of my invention is to provide a blasting machine of thecentrifugal type, in which an abradant material is supplied to themachine and is then centrifugally accelerated and projected by and fromthe machine in a definite pre-selected direction.

Another object of my invention is to provide a blasting machine of thecentrifugal type in which the directional control may be easily andreadily established by controlling the point of feed of the abradantmaterial to an accelerating and throwing part of the machine, such as aradial slinger blade. 7

Another object of my invention is to provide a method of and a structurefor feeding the abradant onto an accelerating surface of the machine, insuch manner that the abradant will approach the accelerating surface ina curved path that will engage the accelerating surface relativelysmoothly and substantially tangentially, so the wearing efiect of theabradant particles on the accelerating surface will be a minimum.

Another object of my invention is to provide a blasting machine of theforegoing character, in which the feeding of the abradant material maybe easily and variably controlled by the operator, to vary both theposition and the quantity of feed, so the quantity of the blastingmaterial will be subject to the control of the operator, withoutexcessive changes in the structural assembly of the machine.

Another object of my invention is to provide a blasting machine in whichmeasured quantities of the abradant material may be supplied to theprojecting or throwing part of the machine, for projection by themachine at a pre-determined point.

One modification of a blasting machine, that is contructed in accordancewith the principles of my invention, consists of a rotatable head orrotor shaped like a wheel and provided with several radially disposedslinger blades. lhe outer ends of the slinger blades are open and theblades are held in, fixed position on a rotor disc or spider. Theabradant material is supplied to the inner end of each slinger bladewhen that blade reaches a pre-determined position in its cylinder.

path of travel, so the abradant material, will be accelerated andprojected and discharged from the outer end of that blade when the blademoves through a pre-determined angle beyond the position at which theabradant material has been supplied to the plate. Since the centrifugalforce acting on the abradant material, to move the material along thesurface of the projecting plate, is relatively constant, the timeinterval required for the abradant material to move from the inner endof the plate to the outer or projecting end of the plate will beuniform. By co-ordinating such time interval of movement of the materialalong the plate with the angle through which the plate will move in thesame period of time, the abradant material may be supplied to the innerend of the blade at the proper angle in advance of the line ofprojection, or discharge, to ensure that the abradant material will bethrown from the rotor at the proper point. 4

The abradant material is fed to the inner ends of each of the radialslinger blades by a distributor through which themachine is suppliedwith the abradant material. The distributor consists of a cylinderdisposed like a hub, con;-

centrically near the inner ends of the blades. The innerends of theblades do not touch the cylinder, as a hub, however. The'cylinder isprovided 'with several passages or openings through the cylinder wall,one passage being adjacent the inner end of each of the blades. Thetransfer of abradant material, through each of those openings, to theassociated slinger blade, is controlled through a valve, at the properpredetermined position.

In this case each valve consists of a pivoted roller nested in alongitudinal groove in the outer surfaceof the cylinder, andcommunicatingwith the transfer opening through the wall of the Theroller is provided with two co-- aXial end journals that are supportedfor rotation in two end bearings that are mounted on the outer surfaceof the cylinder. 7

The roller is provided with a longitudinal groove, or pocket, atone zonein its periphery, where the pocket will communicate with the slot in thecylinder, when and While the roller is in normal or loading position.When the roller is,

turned to unloading position, the pocket is moved away from and out ofcommunication with the slot.

to a slinger blade, the roller of the corresponding associated valve isturned through a suflicient angle to shift the roller pocket away fromthe slot and to unloading position, at which the abradant material inthe pocket is spilled over the edge of the roller pocket in response tocentrifugal force, and the abradant material then falls'onto the slingerblade.

The angular movement of the roller of the valve is controlled through abell-crank that is also pivotally supported on the outer surface of thecylinder. a fork secured on the roller shaft, and'serves to move theroller to either of its operating positions, that is, either to normalloading position, or to operated unloading position.

The other arm of the bell-crank carries a magnetizable plate at its end,so disposed that the plate will pass adjacent to an energized e1ectro-magnetic core structure. When the plate moves into the effectivemagnetic flux field 'of the electro-magnet, the plate is attracted bythe magnet, and is so held as to be retarded momentarily. Suchmomentary, retardation of that arm of the bell-crank imparts an angularmovement to the bell-crank to turn the valve roller through an anglesufiicient to move the roller from loading'position to unloadingposition, and

thereby to spill or feed the abradant material in the pocket of theroller onto the inner end of the associated slinger blade. 7

When the armature plate at the end of the bell-crank is moved out of theeffective magnetic flux 'zone of the electro-magnet, by the continuingrotation of the rotor, centrifugal force acts on the fork-and on theoperating arms of that valve, so the abradant particles discharged bythe roller will move through a curved path onto the blade with arelatively smooth continuous movementthat approaches the surface of theslinger blademore or less as a tangent to the curved path of theabradantmaterials.

Figure 1 is a side view, particularly inrelevation, and partially insection, of a blasting machine rotor' embodying this invention;

Figure 2 is an enlarged longitudinal vertical sectional view, partiallyin elevation, and with parts broken away, to show the distributor on therotating head of the blaster, and the stationary support for the controlelectro-magnet;

Figure 3 is a plan view of the electro-magnet core structure showing thelocation of the control armature;

One arm of the bell-crank fits into of the valve roller with a portionof the valve roller and of the distributor cylinder broken away, to showthe shape of the pocket in the roller, and its relative dispositionadjacent the slot in the cylinder; and

Figure 9 is a transverse view of the cylinder and the roller, with theroller shown in loading and in unloading positions, to illustrate themanner inwhich the discharged particles'from the roller move in a curvedpath onto the slinger blade.

As shown in the drawings, a blasting machine I I], constructed inaccordance with the principles of my invention, is shown as comprising,briefly, a rotatablehead or rotor I I, mounted at one end of a driveshaft I2 that is supported, for rotation, between two supportingbearings I3 and I4. The drive shaft I2 is provided with a suitabledriving pulley I 5 at the other end of the shaft, by means of which theshaft may be driven from any suitable source of motive power, to rotatethe shaft and the rotor at high speed. I

The rotatable head. I I comprises briefly a spider, or back disc plateI6, provided with a hub I1 by means of which the disc plate may be keyedto the drive shaft I2 with a suitable means such as a key I8. The discI6 carries several slinger blades 20 that are radially disposed on, and

fixedly secured to, the disc I6, by anchoring plates 2| that are boltedto the disc I6 to hold the slinger blades in place by fitting over edgeflanges 22 on the edges of the blades 20 that rest against the disc I6.The anchoring plates are anchored to the disc I6 by bolts 23.

The drive shaft is driven at a relatively high speed to rotatethe discI6 and the rotor slinger blades 20 at the same high angular velocity, inorder to impart a high velocity to the abradant material by the timeitis moved out. to the end of the respective slinger blades andprojected and discharged by and from those blades in a predetermineddirection, against an object or surface that is to be b1asted.

Figure 4' is an end elevational view, partially schematic, of thedistributor cylinder, showing the valve rollers,the controlelectro-magnet for the valve rollers, and the slinger blades shown inpart, to show their'relative location adjacent the valve rollers; Figure5 is a plan development of a part of a roller, its operating arm, andthe associated bellcrank;' 'Figure 6 is a partial and broken end View ofa slinger blade showing its disposition on its supporting disc; 7 i 7Figure '7 is an end elevational view of a roller bearing for a valveroller, asnested in a groove inthe distributor cylinder;

; Figure 8 is a transverse view through the'shaft' The acceleratingsurface 25 of each slinger blade '20 is relatively smooth andcontinuous, so the abradant material can move freely along the fulllength of the slinger blade without inter-' ference of any kind thatwould diminish the momentum of the accelerated abradant material,

and absorb some of the kinetic energy from that material. The freeuninterrupted passage of the abradant matterial along the inner surfaceof the slinger blade tends to maintain a uniformity of traveling timeinterval of the abradant material on each one of the blades, so thedischarge point will be uniform and constant on the several blades, whenthe several blades are fed with the abradant material at the same pointon the orbital path traversed by the inner ends of those blades.

The abradant material is fed to the inner ends of the blades 20 by andthrough a distributor 30.

As shown in the drawings, the distributor 30 comprises a supply cylinder31 co-axially secured to the end of the drive shaft I2 andconcentrically disposed in a centrallopening on the rotor adjacent theinner ends of the slinger blades. The distributor cylinder 3I isprovided with four slotted openings or transfer passages 32, 33, 34, and35. The transfer passages from 32 to 35 inclusive are equally spacedaround the periphery of the cylinder, each passage being located in thezone generally adjacent but slightly in advance of the inner end of anassociated slinger blade or plate- 20.} Each'slotted passage 32 to 35 issub;

stantially rectangular in cross-section andhas substantially straightradial side walls to permit the abradant material to move readilythrough those openings from the inside of the cylinder 3|. The outersurface of the cylinder 3| is also provided with shallow fluted grooves36 to 39, inclusive each axially and symmetrically aligned with thecorresponding slotted transfer passage 32 to 35 inclusive. The shallowgrooves 36 to 39 are of greater length than the slotted transferpassages 32 to 35, but less than the full length of the cylinder 3|.

The fluted grooves 36 to 39,.inclusive, are respectively provided toreceive a control roller 48 which serves as a control valve to transfera measured amount of abradant material from the cylinder distributor toits associated radial slinger plate 28.

The roller 40- is provided with two end shafts or journals 4| and. 42,and with a long recess or pocket 43 at a central region on itsperipheral surface. The pocket 43 is substantially triangular incross-section, and the length of the pocket 43 is less than the lengthof the roller body, but

is preferably greater thanthe length of any of the slotted transferpassages 32 to 35, through the wall of cylinder 3|.

The roller 46 and the arcuate or fluted groove surface 36 in. thecylinder wall are concentric so the roller will substantially nest orseat itself in the groove 36.

Each roller 4!) is mounted for angular movement on the distributorcylinder 3|, and is supported on the distributor cylinder 3! between twoball bearings 44 and 45 that are anchored to the cylinder 3| by suitableanchoring straps 41 and 48. The straps 41 and 48 may be welded to thecylinder 3| or secured thereto by bolts.

In order to impart a turning movement to the roller 48 to move thepocket 43 from its normal loading position, where it communicates withthe transfer passage 32, to its unloading position, at which the pocket43 will be separated and disconnected from the transfer passage 32, anoperating fork58 is keyed to roller shaft 4|.

The operating fork 58 is illustrated briefly as comprising an upperhousing section 5| and a lower housing section 52 respectively providedwith fork arms 53 and 54. The two body sections 5! and 52 of the forkare clamped together by bolts 55 and 56 and keyed to the shaft 4| of theroller" by a key 51.

The fork 58 is arranged to be operated by means of a bell-crank 68,having an operating arm 6|, and a control arm 62. is pivotally supportedfor its angular movement, between two spaced side walls 63 and 64 of abracket 65, that is provided with a base 66 that is suitably secured tothe distributor cylinder 3|, either by Welding or by bolts 61.

The operating arm 6| of the bell-crank 68 is provided with a small fork68 that supports an anti-friction roller or roller bearing 69 on a smallpivot shaft 18.

The roller or roller bearing 69 fits in the fork 50 on the shaft of thevalve roller 46. Whenthe valve roller 40 is in normal loading position,with its pocket communicating with the transfer pase sage through thewall of the distributor cylinder 3|, the fork 50 and the bell-crank 68will be in the position shown in Figure 4, in their respective outermostlimit positions.

Disregarding friction for the moment, the valve roller fork 50 andthe-bell-crank arm 6| will be biased towards their outermost positionsby the The bell-crank centrifugal force developed during rotation of therotor and the distributor cylinder. In order to limit the outwardmovement of the fork 50 and of the bell-crank arm. 6|, a stop lug 1|extends from the walls'of the bearing bracket 65, for the bell-crankpivot shaft, to serve as a stop to define the outer limit positionof thebell crank arm 6| slightly behind the radius line from the center axis.

of the distributor cylinder 3|. through the axis of the bell crank. I

The outer end of the bell-crank arm 62 carries a magnetizable plate 15that is to serve as an armature to be attracted by an adjacent controlelectro-magnet 1'6. The armature plate 15 is symmetrically supported onthe bell crank arm 62, and the center of gravity on the bell-crank'arm62 and the plate 15 is therefore also behind the radius line from thecenter of the rotor distributor axis through the pivot axis of thebell-crank. Consequently, during rotation of the rotor, centrifugalforce further tends to turn the bell-crank to move the'bell-crank arm 6|to its outermost position, and thereby move the valve. roller '40 toloading position.

r The control electro-magnet 16 is shown as comprising a magnetic corestructure 11 of substantially U-shape with an energizing coil 18. Thecore structure 11 has two pole faces Biland 8| that are separated by anair gap 82. The two pole faces and 8| are partially recessed to embodyinwardly facing shoulders 83 and 84 that are to be directly underneaththe armature plate 15 at the end of the bell-crank during rotation ofthe rotor. The air gap' space between the lower or outer surface of thearmature'plate 15 and the shoulder surfaces 83' and 84 of theelectro-magnet may thus be made'relatively small.

The two faces also embody the outer side walls 85 and 86 at the outeredges of the shoulders 83 and 84. The space between the inner wallsurfaces of the side walls 85 and 86 is slightly larger pivotal than thecorresponding dimensions of the armatureplate 15 when the armature plateis moved through that space at the endof the bell crank, duringrotation.

By means of the shoulder and side wall arrangement, a magneticattractive force is impressed upon the armature plate 15 irrespective ofits position during its turning movement on its pivotally supportedbell-crank.

In order to permit sufficient clearance between the armature plate 15,at the end of the bellcrank, and the shoulder surfaces 83 and 84, theelectro-magnet is spaced a suflicient distance away from the main axisof rotation of the rotor to be free of the armature plate 15 when thearmature plate is in its furthermost radially extended position.

The angle through which the bell-crank must be moved, by the retardingmagnetic friction force of the electro-magnet on the armature plate 15,depends upon the angle through which the valve roller must be turned, toshift the pocket on the roller from the normal loading position of thevalve to its unloading -position, at which the abradant particles arereleased from the pocket of theroller to move onto the adjacent surfacof theslinger blade.

As shown in Figure 9, when the valve is in the normal loading position,the bottom or lag ging surface of the pocket in the valve roller isinclined-slightly upwardly from aline through i the bottomcorner of thepocket and parallel to -a tangent to the cylinder 3!.

In order to permit the abradant materials or particles to fall free fromthe pocketonto the slinger blade, when the valve is moved to unloadingposition, the roller should be moved through a sufficient angle to bringthe bottom surface of the pocket to an angle below the tangent parallel,as shown in Figure '9.

c -That angle constitutes the operating angle of the valve anddetermines the angle through which the fork 50 must be moved by thebell-crank to establish a desired operation of the valve to feedabradant to a slinger plate.

Since turningmovement of the fork will tend to turn the upper fork arm53 towards the cylinder surface, which would limit the-fork movement,the initial or normal positionof the fork during the loading operationof the valve will be somewhat underinclined from the horizontal line tothe valve roller axis, when the line between the valve axis and therotor axis is considered vertical. 'of the valve roller and'the pivotalaxis of the The distance between the axis which the particles may movewith a minimum of friction in response to the centrifugal force that ismoving them outwardly along the slinger plates surfaces.

Each slinger blade or plate is supplied with the abradant material fromits'own valve, and, in order to reduce attrition of the plate to aminimum, each plate is mounted a short distance behind its valve so thetrajectory of the abradant particles, whenthey leave the valve'roller,will approach the slinger blade surface as an asymptote or substantialtangent. I 7

For that reason, it is alsotherefore preferable to supply the abradantparticles at a zone of low speed, which is the center of rotation, andthen to feed the abradant particles from the central low-velocity zoneof the rotor onto the slinger blades or plates, in the same generaldirection which those particles are to take as they are fed to theplates for acceleration and projection. By means of the constructionillustrated, each valve roller is provided with a substantially measuredamount of the abradant particle to be supplied to each slinger bladeduring each opera tion. The dimensions of the pocket may be variedaccording to the quantity or volume of each charge that it is to besupplied to each blade. In order to permit easy rotation of the roller 7of the valve to unloading position, the pocket in the roller is madesomewhat longer on both sides than the slot in the cylinder wall, andthe pocket is centrally located relative to transfer passage 32 in thecylinder wall, through which the abradant material is supplied to thepocket of the valve. Consequently, when the valve roller isturnedthrough the'small angle to unloading position, someof the abradantparticles in: the

pocket shift over towards the ends of the pocket and remove thesustaining pressure from the central portion'of the charge of abradantin the middle zone of the pocket.

In order to control the point at which the valve rollers will beoperated to discharge the quantity of abradant material in each pocket,the electro-magnet is mounted on a ring bracket that is concentric withthe rotor. The electromagnet is adjustably mounted on the ring bracket90 so it may be adjustably positioned on .the ring bracket, and thenfixed in such position which the entire blasting mechanism is mounted.

The trough support 92 is also provided with a ring shaped bracket 93,that serves as a stationary hearing within which the ring bracket 99,for the electro-magnet, may be rotatably supported, for short angularadjustments of the supporting co-axial shaft 9|, by means of a handle 94on the outer end of the shaft 9|.

When a substantial angular adjustment of the electro-magnet is desired,the entire bracket 95 for the electro-magnet is adjustably shifted onthe ring bracket 9!}, and then securely tightened in place by a suitablebolt 91. v

For simplicity, the electro-magnet is shown as supported on a'shelf atthe lower'end of the adjustable bracket 95 that is mounted onthe ring90. Since the entire adjusting and supporting mechanism fortheelectro-magnet is co-axially disposed with respect to the main cylinderdistributor, any adjustment of the electro-magnet will keep it in properposition with respect to the armature plates associated with each of thevalve rollers.

As shown in Figure 4, the inwardly extending shoulders on the side wallsof the electro-magnet are concave and have a curvature that isconcentric with the distributor cylinder, so the armature platesmay movefreely between the two pole pieces of the electro-magnet.

As illustrated in Figures 8 and 9, the pocket in each roller, when inloading position, is directly underneath the slot'inthe distributorcylinder, so it may receive a charge of abradant material. When thecylinder is turned to unloading position, as shown in Figure 9, theabradant material spills out of the roller pocket in a trailing slipstream 99, in a substantially parabolic curved path, that approaches theaccelerating surface of the slinger blade directly behind it,-with asmooth tangential contact.

By thus arranging the valve, slightly in advance of the slinger blade,so the material may be supplied from the valve to the slinger blade in apath of movement having substantially no component, or a very smallcomponent, in a direction perpendicular to the surface of the slingerblade, the effects of attrition of the abradant material on the slingerblade surfaces is reduced to a minimum.

As shown in Figures 4' and 6, the slinger blade 7 20 is arranged to beheld in position on and against the main back disc plate l6, by the onthe edge of the plate that rests against the disc. The radial edgesurfaces, of the slinger blade 20, that is engaged by the anchoringplate 2I, may be slightly angularly convergent, with the correspondingsurfaces or edges on the anchoring plate 2| divergent, outward from thecenter of rotation, so the slinger blades will be held by a wedgingaction between the anchoring plates 2I.

- As shown in Figure l, the abradant material is supplied to thedistributor cylinder through a conduit 98 that constitutes the lower endof a feed hopper. This conduit 98 extends through the space in thetrough 92 and then through the ring bracket 90 and the bearing bracket93 to the distributing cylinder.

For extensive angular adjustments of the electro-magnet, the supportingbracket 95 for the electro-magnet may be loosened at the bolt 91, andthe bracket 95 then adjustably shifted to substantially the positiondesired on the ring bracket 90, and the bolt then re-tightened to lockthe bracket 95 in position on the supporting ring bracket 90. Finerangular adjustments of the ring bracket 90 may then be made to locatethe electro-magnet, by means of the handle on the shaft 9| that issecured to the supporting ring bracket 90 on which the bracket 95 issecured. By such adjustable positioning of the magnet, the direction ofthe stream of discharged abradant may be controlled.

As shown in Figure 2, the distributor cylinder and the valve rollers aresupported on the end of the main shaft 12 by means of a cylinder capbracket I00.

The cylinder cap bracket I is provided with a portion IOI that fits overthe end of the main drive shaft I2 and that is keyed thereto by a keyI02. A similar cylindrical portion I03 extending in the oppositedirection extends over one end of the distributor cylinder, and issecured thereto by suitable bolts I05.

The cylinder cap I00 is secured to the main drive shaft I2 by an anchorbolt I06 which is threaded into the end of the drive shaft I2, andpresses against a pressure plate I01 that is concentrically seated onand against the center wall I04 of the cylindrical bracket I00. A lockwasher I08 holds the bolt I06 against casual displacement.

As shown in Figure 1 and in Figure 2, the inner end edge of the slingerblade is spaced a short distance from the distributor cylinder, and ashort distance behind the associated valve roller. With this arrangementthe distributor cylinder and its control rollers may be handled as aunit for assembly and for removal, if necessary.

As is shown in Figure 1, the edge 20a of the slinger blade is spacedsufiiciently from the main rotor disc IE to bring that edge 20a out farenough to receive all of the abradant material that is spilled out ofthe pocket of the valve roller.

My invention is not limited to the specific details of construction thatare illustrated since various modifications might be made in thosevarious details without departing from spirit and scope of the inventionas set forth in the appended claims.

I claim as my invention:

1. A blasting machine comprising a rotor having a plurality of radialslinger blades; means for supplying abradant particles to the machine;and means individually associated with each blade for measuring out aquantity of the abradant particles and for feeding those measuredparticles to the associated blade; and electro-magnetic means adjustablypositionable adjacent the rotor to operate the feeding means at apre-determined point, thereby to control the zone of discharge from theblades.

2. A blasting machine comprising a rotor having a plurality of radialslinger blades; means for supplying abradant particles to the machine; adistributor including a central cylinder, concentric with the radialblades for receiving the particles, and spaced valves on the cylinder,one valve for each blade, fortransferring particles from the cylinder tothe associated blade; and electr c-magnetic means adjustablypositionable to operate the valve to feed the particles to the blades ata selected point of the pathof the blades.

3. A blasting machine comprising a rotor having a plurality of radialslinger blades; means for supplying, abradant particles to the ma chine;a distributor including a central cylinder concentric with the radialblades for receiving the'particles, and spaced valves on the cylinder,one valve for each blade, for transferring particles from the cylinderto the associated blade; each said valve comprising a roller with endshafts, the roller being pivotally supported and being seated in alongitudinal groove of arcuate section on the outer surface of thecylinder, with a slot in the groove extending through the cylinder wall,the roller having a longitudinal pocket registering with the slot in thecylinder wall when the roller is in particle-receivingposi tion, andbeing out of communication with the slot when oscillated tounloading'position; bearings on the cylinder to support the roller forrotation; means normally biasing the roller to receiving position; andmeans for angularly moving the roller to unloading position.

4. A blasting machine comprising a rotor having radial slinger blades;'a distributor cylinder concentrically disposed and secured to therotor; the cylinder having, in its outer surface, adjacent the inner endof each blade, a longitudinal fluted groove with a shorter centralradial slot through the cylinder wall; means for supplying abradantparticles to the inside of the cylinder; and means for transferringabradant particles from the cylinder to each slinger blade, said meansconsisting of a roller to seat and fit into the fluted groove, theroller having a longitudinal pocket in its periphery to register withthe slot in the cylinder groove and to receive a quantity of abradantparticles while in such registering loading position, the roller beingsupported for angular movement to move the roller pocket tonon-communicating unloading position and to permit the particles to becentrifuged out of the pocket onto the associated blade, to be thenceaccelerated and thrown by and from the blade;

means for pivotally supporting the roller; and 7 means for moving theroller to its loading and to its unloading positions.

5. A blasting machine as in claim 4, in which the pocket in the rolleris substantially triangular in section, with one side of the triangledisposed to forma departing angle with a. tangent to the cylinder, whenthe roller is turned to unloading position.

6. A blasting machine as in claim 4, in which the roller-moving meansinclude a pivoted arm supported on the cylinder and provided and adaptedto turn the roller to unloading position;

and an electro-magnet for actuating the pivoted arm to turn the rollerto that unloading position.

7. A blasting machine as in claim 4, in which the roller-moving meansincludea pivoted arm to turn the roller; an electro-magnet to actuatethe arm; and means for adjustably positioning the electro-magnet topro-determine the posi-, tion at which the arm will be actuated to turnthe roller to unloading position, to feed abradant to the associatedslinger blade.

8. A blasting machine as in claim 4, in which the slot in the cylindergroove is shorter than the pocket in the roller to provide over-flowspaces for the charge of abradant in the pocket, when the roller isturned to move its pocket froin the slot.

9. A blasting machine comprising a rotor for projecting an abradantmaterial centrifugally at high velocity from several spaced peripheralzones; a central cylindrical container for receiving a supply ofabradant material, and secured to the rotor to rotate with it; auxiliaryvessels for receiving a quantity of the abradant from the container; andelectro-magnetic means for tilting the vessels for transferring all orpart of such quantity to the rotor at a pre-determined position of therotor to enable the abradant to be shifted to, and thrown from, theperipheral zones of the rotor, at a pre-determined point in theperipheral path.

10. A blasting machine comprising a rotor having means establishingseveral spaced passageways from th center of the rotor to the periphery;a cylindrical container concentrically disposed in the center of therotor and secured to rotate therewith, said container having openingsthrough its wall to feed the several spaced pas-.

sageways in the rotor; means for supplying abradant particles to thecontainer; and means pivotally supported on the outer surface of thecontainer and movable to a loading position to receive a quantity ofparticles from the container, and movable to supply the particles to thepassagewayswhile closing the feeding openings; means biasing the pivotedmeans to loading position; and means adjustably positionable to shiftthe pivoted means to unloading position.

11. A blasting machine comprising a rotor having a plurality of radialslinger blades spaced to provide a central opening; a distributorconsisting of a cylinder concentrically disposed in the opening toreceive a supply of abradant particles to be fed to the blades; anorifice in the cylinder wall adjacent the inner end of each blade; avalve for the orifice, said valve embodying an element pivotallysupported on the cylinder on an axis parallel to the cylinder axis; andmeans to operate the valve element through a small angle to an unloadingposition to permit some abradant particles to pass out through theorifice while controlling the orifice to limit the passage of abradanttherethrough, said operating means consisting of a pivoted bell-crank onthe cylinder, the bell-crank having one arm disposed to turn the valvethrough said angle and having the other arm normally extending in ageneral radial direction from the main rotor axis, that arm beingadapted to be operated, externally and independently of the rotor,through an angle to correspondingly turn the valve element to unloadingposition. 7

12. A blasting machine as in claim 11, in which an electro-magnet isprovidedrto be adjustably positioned adjacent the paths of travel of theouter end of the bell-crank to attract and to retard that end of thebell-crank, and thereby to apply an effective turning force that willoscillate the bell-crank through the desired angle to turn the valveelement.

' JULIUS E. FOSTER.

